Scheduling method and apparatus in a relay communication system

ABSTRACT

Disclosed are a packet scheduling method and apparatus in a relay network. A scheduling method of a relay station in a relay communication system includes: receiving information regarding an amount of generated data to be transmitted to a user from a base station; estimating the size of a queue of the base station storing the data to be transmitted to the user based on the amount of generated data received from the base station; obtaining the size of a virtual queue in which overall data to be transmitted to a user with reference to the estimated size of the queue of the base station and the size of a queue of the relay station storing data to be transmitted to a user; performing scheduling to allocate resource based on the size of the virtual queue; and transmitting data to the user based on the scheduling results.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2010/005050, filed on Jul. 30, 2010,which claims the benefit of earlier filing date and right of priority toKorean Application No. 10-2009-0122774, filed on Dec. 10, 2009, and alsoclaims the benefit of U.S. Provisional Application Ser. No. 61/232,462,filed on Aug. 9, 2009, the contents of which are all incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a scheduling method and apparatus in arelay system and,

more particularly, to a scheduling method and apparatus of a relay forensuring optimum throughput and fairness among users.

BACKGROUND ART

A general cellular network configures a radio communication link havinghigh mutual reliability through a centralized cell design in whichcommunication is performed through a direct link between a base stationand a terminal in a cell covered by the base station.

However, recently, communication networks tend to use a high servicefrequency band, and the radius of cells tends to be reduced in order tosupport high speed communication and accommodate a larger amount ofcalls, so the use of the existing centralized cellular radio networkscheme as it is in the future involves many problems. Namely, since thelocation of a base station is fixed, flexibility of a radio linkconfiguration deteriorates, having a difficulty in providing aneffective communication service in a radio environment in which atraffic distribution or a call request amount are excessively changed.

Thus, a next-generation communication system should be distributedlycontrolled and established and actively cope with a change in anenvironment such as an additional installation of a new base station,and as a solution to the foregoing problems, a relay system has beenproposed. A relay system is advantageous in that it extends cell servicecoverage by covering a partial shadow area generated in a cell regionand increases a system capacity. In addition, a relay (referred to as a‘relay station’, hereinafter) may be used at an initial situation whenservice requests are relatively low to reduce the burden of an initialinstallation cost.

In a system using a relay station, a user to which resource is directlyallocated through a base station and a user to which resource isallocated by way of the relay station coexist. In this case, the basestation is supposed to perform scheduling in consideration of all of theamount of packets served by the base station, the amount of packetsserved by the relay station, the size of a queue of the base station,and the size of a queue of the relay station, to thus optimize a packettransfer rate and equally allocate resources to all the users. However,currently, a scheduling method in consideration of the foregoing mattershas yet to be proposed for such a relay system.

DISCLOSURE Technical Problem

Therefore, an object of the present invention is to provide a schedulingmethod and

apparatus of a relay for ensuring optimum throughput and fairness amongusers in a relay communication system.

Technical Solution

According to an aspect of the present invention, there is provided ascheduling method of a relay station in a relay communication system,

including: receiving information regarding an amount of generated datato be transmitted to a user from a base station; estimating the size ofa queue of the base station storing the data to be transmitted to theuser based on the amount of generated data received from the basestation; obtaining the size of a virtual queue in which overall data tobe transmitted to a user with reference to the estimated size of thequeue of the base station and the size of a queue of the relay stationstoring data to be transmitted to a user; performing scheduling toallocate resource based on the size of the virtual queue; andtransmitting data to the user based on the scheduling results.

According to another aspect of the present invention, there is provideda scheduling method of a relay station in a relay communication system,including: periodically receiving information regarding the amount ofgenerated data to be transmitted to a user from a base station toestimate the size of a queue of the base station storing data to betransmitted to a user; periodically receiving the information regardingthe size of the queue of the base station storing the data to betransmitted to the user from the base station to update the estimatedsize of the queue of the base station; obtaining the size of a virtualqueue storing overall data to be transmitted to a user with reference tothe updated size of the queue of the base station and the size of aqueue of the relay station storing data to be transmitted to a user;performing scheduling to allocate resource based on the size of thevirtual queue; and transmitting data to the user based on the schedulingresults.

According to another aspect of the present invention, there is provideda scheduling method of a relay station in a relay communication system,including: receiving information regarding the size of a queue of a basestation storing data to be transmitted to a user from the base stationwhen the size of the queue of the base station corresponds with apredetermined reference; obtaining the size of a virtual queue storingoverall data to be transmitted to a user with reference to theinformation regarding the size of the queue received from the basestation and the size of a queue of the relay station storing data to betransmitted to a user; performing scheduling to allocate resource basedon the size of the virtual queue; and transmitting data to the userbased on the scheduling results.

According to another aspect of the present invention, there is provideda scheduling method of a relay station in a relay communication system,including: receiving user index information indicating that the amountof data to be transmitted to a user exceeds a certain reference, from abase station; determining a priority level of resource allocation ofeach user with reference to a user index information received from thebase station and the size of a queue of the relay station storing datato be transmitted to a user; and transmitting data to the user based onthe scheduling results.

According to another aspect of the present invention, there is provideda scheduling apparatus of a relay station in a relay communicationsystem, including: a receiver configured to receive the amount ofgenerated data to be transmitted to a user and information regarding thesize of queue of a base station storing data to be transmitted to theuser from the base station; a virtual queue estimator configured toestimate the size of the queue of the base station storing the data tobe transmitted to the user based on the amount of generated datareceived from the base station and determine the size of a virtual queuestoring overall data to be transmitted to a user with reference to theestimated size of the queue of the base station and the size of a queueof the relay station storing data to be transmitted to a user; ascheduler configured to perform scheduling to allocate resource based onthe size of the virtual queue determined by the virtual queue estimator;and a transmitter configured to transmit data to the user based on thescheduling results of the scheduler.

Advantageous Effects

According to embodiments of the present invention, fairness between auser who is provided with a packet service from a base station through adirect link with the base station an a user provided with a packetservice from a relay station through a relay link is guaranteed, and forthe user who receives a packet through the relay link, delay in a packetreception as in the related art can be reduced, enhancing delayperformance.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view conceptually showing packet scheduling of a basestation and a relay station in a wireless relay network environment.

FIG. 2 is a view showing a sequential scheduling process according to afirst embodiment of the present invention.

FIG. 3 is a view showing a sequential scheduling process according to asecond embodiment of the present invention.

FIG. 4 is a view showing a sequential scheduling process according to athird embodiment of the present invention.

FIG. 5 is a view showing a sequential scheduling process according to afourth embodiment of the present invention.

FIG. 6 is a schematic block diagram of a scheduling apparatus of a relaycommunication system according to an embodiment of the presentinvention.

FIGS. 7 and 8 are graphs showing performance comparison results showingdelay violation probability of a user according to a scheduling scheme.

BEST MODES

The exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which like numbers referto like elements throughout. In describing the present invention, if adetailed explanation for a related known function or construction isconsidered to unnecessarily divert the gist of the present invention,such explanation has been omitted but would be understood by thoseskilled in the art. The accompanying drawings of the present inventionaim to facilitate understanding of the present invention and should notbe construed as limited to the accompanying drawings.

Hereafter, a term of a user (or a terminal) is used, and the user may becalled by other names such as UT (User Terminal), SS (SubscriberStation), UE (User Equipment), ME (Mobile Equipment), or MS (MobileStation). Also, the terminal may be a portable device having acommunication function such as a mobile phone, a PDA, a smart phone, anotebook computer, or the like, or a device which is not portable, suchas a PC, a vehicle-mount device.

FIG. 1 is a view conceptually showing packet scheduling of a basestation (BS) and a relay station (RS) in a wireless relay networkenvironment.

As shown in FIG. 1, in a relay communication system in which a relaystation 120 plays a relay role between a base station 110 and aplurality of users (user 1, . . . , user K, user K+1, . . . , user L),packets 10, 20, 30, 40 of each user arrive at the base station 110through a backbone network, the corresponding packets are stored in aqueue Q^(BS) for each user in the base station 110.

With reference to FIG. 1, it is assumed that communication is performedaccording a time-division scheme in which packets of only one user aretransmitted between the base station 110 and the relay station 120, forthe sake of explanation, and also, it is assumed that the base station110 transmits packets to the first user (user 1) to the Kth user (userK) through the relay station 120 and the base station 110 directlytransmits packets to the (K+1)th user (user K+1) to Lth user (user L).However, the present invention is not limited to the environment asillustrated in FIG. 1 and a case in which packets of several users maybe simultaneously transmitted between the base station 110 and the relaystation 120 may also be included.

When a transfer rate of a channel link between the base station 110 andthe relay station 120 in which a packet of the Kth user is transmittedis R_(Bk)(n) and a transfer rate of a channel link between the relaystation 120 and the user K in which the packet of the Kth user istransmitted is R_(Rk)(n), since the channel link between the basestation 110 and the relay station 120 is common to the first user(user 1) to the Kth user (user K), so it may be expressed such thatR_(Bk)(n)=R_(BR)(n), (k=1, 2, 3, . . . , K).

Also, when the amount of packets of the Kth user transferred from thebase station 110 is A_(k) ^(BS)(n), the amount of packets of the Kthuser transferred from the base station 110 to the relay station 120 isA_(k) ^(RS)(n), and the amount of packets of the Kth user accumulated ina queue within the relay station 120 is Q_(k) ^(BS)(n), a queue of thebase station 110 in which packets to be transmitted to the Kth user at(n+1)th time are accumulated can be expressed by Equation 1 shown below:Q _(k) ^(BS)(n+1)=max(Q _(k) ^(BS)(n)−S _(k) ^(BS)(n),0)+A _(k)^(BS)(n)  [Equation 1]

In Equation 1, S_(k) ^(BS)(n) is the amount of packets served by thebase station 110.

Also, the queue of the relay station 120 in which packets to betransmitted to the Kth user at the (n+1)th time can be expressed byEquation 2 shown below:Q _(k) ^(RS)(n+1)=max(Q _(k) ^(RS)(n)−S _(k) ^(RS)(n),0)+A _(k)^(RS)(n)  [Equation 2]

In Equation 2, S_(k) ^(RS)(n) is the amount of packets served by therelay station 120.

Here, when it is assumed that the base station 110 performs schedulingin a max backlog manner, the base station 110 performs scheduling asexpressed by Equation 3 and Equation 4 shown below:

$\begin{matrix}{{k^{BS}(n)} = {\arg\;{\max\limits_{{k = 1},\ldots,L}{\gamma_{k}{R_{BK}(n)}{Q_{k}^{BS}(n)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack \\{{S_{k}^{BS}(n)} = {{A_{k}^{RS}(n)} = {\min\left( {{{R_{BR}(n)}1_{k = {k^{BS}{(n)}}}},{Q_{k}^{BS}(n)}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 3 and Equation 4, γ_(k) is a constant and 1_(k=k) _(BS)_((n)) is an indicator function having a value 1 when K=k^(BS)(n) and avalue 0 when k≠k^(BS)(n).

In Equation 4, the amount of packets S_(k) ^(BS)(n) served by the basestation 110 is equal to the amount of packets A_(k) ^(RS)(n) arriving atthe relay station 120, and has a smaller value among a link transferrate of the selected user and the size of the queue.

Thus, packets from the base station 110 are not transmitted to a userwho has not been selected, and when the size of the queue is smallerthan the link transfer rate, only packets accumulated in the queue ofthe base station 110 are transmitted.

Similarly, when it is assumed that the relay station 120 performsscheduling in a max backlog manner, the relay station 120 performsscheduling as expressed by Equation 5 and Equation 6 shown below:

$\begin{matrix}{{k^{RS}(n)} = {\arg\;{\max\limits_{{k = 1},\mspace{14mu}\ldots\mspace{14mu},K}{\gamma_{k}{R_{RK}(n)}{Q_{k}^{RS}(n)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{S_{k}^{RS}(n)} = {\min\left( {{{R_{Rk}(n)}1_{k = {k^{RS}{(n)}}}},{Q_{k}^{RS}(n)}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

The scheduling performed by the base station 110 and the relay station120 as expressed by Equation 3 to Equation 6 is a scheme ofpreferentially selecting a user who has the largest product of thetransfer rate of the current link and the size of the queue andallocating resource thereto. Thus, in a sense that the user having thelargest backlog is given preference, the scheme is called a max backlogscheduling scheme.

Meanwhile, when it is assumed that the base station 110 performsscheduling based on a max differential backlog scheme, the base station110 performs scheduling as expressed by Equation 7 and Equation 8 shownbelow:

$\begin{matrix}{{{k^{BS}(n)} = {\arg\;{\max\limits_{k\;}{\gamma_{k}{R_{Bk}(n)}{Q_{k}(n)}}}}}{{Q_{k}(n)} = \left\{ \begin{matrix}{{{Q_{k}^{BS}(n)} - {Q_{k}^{RS}(n)}},} & {{k = 1},2,\ldots\mspace{14mu},K} \\{{Q_{k}^{BS}(n)},} & {{k = {K + 1}},\ldots\mspace{14mu},L}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack \\{{S_{k}^{BS}(n)} = {{A_{k}^{RS}(n)} = {\min\left( {{{R_{BR}(n)}1_{k = {k^{BS}{(n)}}}},{Q_{k}^{BS}(n)}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Also, when it is assumed that the relay station 120 performs schedulingbased on the max differential backlog scheme, the relay station 120performs scheduling in the same manner as that of Equation 5 andEquation 6 as discussed above. Like the state of the queue of Equation7, the max differential backlog type scheduling scheme is a scheme ofallocating resource, starting from a user given priority because hisvalue obtained by subtracting the size of the queue of the relay station120 from the size of the queue in which the packets accumulated in thebase station are stored is the largest, among the respective users.Thus, when the system can be made to become stable in consideration ofthe amount of packets arriving from a backbone network and a state of aradio channel, the system can become stable by using the max differentbacklog type scheduling, and it may correspond to a scheduling schemefor ensuring an optimum transfer rate (throughput optimal).

However, referring to the scheduling scheme described through Equation 3to Equation 8, a scheduling metric of the users (user 1, . . . , user K)to which packets are transferred through the relay station 120 from thebase station 110 and that of the users (user K+1, . . . , user L) towhich packets are transmitted through a direct link from the basestation 110 are different, so, in comparison to the users to whichpackets are transmitted through the direct link, the users to whichpackets are transmitted through the relay station 120 are at adisadvantage, in terms of resource allocation.

Hereinafter, a scheduling method of the relay station 120 capable ofincreasing fairness between a user to which a packet is transmittedthrough a direct link and a user to which a packet is transmittedthrough the relay station 120 and enhancing packet reception delayperformance of a user to which a packet is transmitted through the relaystation 120 will be described.

First, the base station 110 performs scheduling in such manners asexpressed by Equation 3 and Equation 4 above.

The relay station 120, employing the scheme of preferentially allocatingresource to a user whose sum of the queue of the base station and thequeue of the relay station is large, performs scheduling in such mannersas expressed by Equation 9 and Equation 10.

$\begin{matrix}{{\gamma^{RS}(n)} = {\arg\;{\max\limits_{{k = 1},\;\ldots\;,K}{\gamma_{k}{R_{Rk}(n)}\left( {{Q_{k}^{BS}(n)} + {Q_{k}^{RS}(n)}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack \\{{S_{k\;}^{RS}(n)} = {\min\left( {{{R_{Rk}(n)}1_{k = {k^{RS}{(n)}}}},{Q_{k}^{RS}(n)}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Referring to the state of the queue of Equation 9, when the sum of thequeue of the base station and the queue of the relay station is avirtual queen, it can be seen that resource is preferentially allocatedto a user having the largest virtual queue. According to the schedulingscheme, when it is assumed that the queue of the base station 110 in acellular system without the relay station 120 is a virtual queue (Q_(k)^(BS)(n)+Q_(k) ^(RS)(n)), scheduling is performed on the packetsaccumulated in the queue of the base station. The scheduling scheme ofEquation 9 and Equation 10 will be referred to as max total backlogscheduling hereinafter.

In the case of the max differential backlog scheduling of Equation 7 andEquation 8 as discussed above, when the base station 110 performsscheduling, the scheduling is performed unfairly between the userthrough the relay station and the user connected by the direct link, butin the case of the max total backlog scheduling scheme of Equation 9 andEquation 10, since scheduling is performed without discriminating theuser connected to the base station 110 by way of the relay station 120and the user connected to the base station 110 through a direct link,resource can be allocated fairly.

Hereinafter, the scheduling process of the relay station forimplementing the max total backlog scheduling as expressed in Equation 9and Equation 10 will be described.

FIG. 2 is a view showing a sequential scheduling process according to afirst embodiment of the present invention.

The base station 110 measures the amount of generated data to betransmitted to each user for which a link is established through therelay station, and transmits information regarding the amount ofgenerated data of each user to the relay station 120 (S201).

According to an embodiment of the present invention, the informationregarding the amount of generated data of each user is informationregarding an average arrival rate Ã_(k) ^(BS)(n) of packets to betransferred to each user or a traffic generation rate of each user, andthe base station 110 may measure the average arrival rate or the trafficgeneration rate of each user and periodically or randomly transmit thesame to the relay station 120.

Upon receiving the information regarding the amount of generated data ofeach user from the base station 110, the relay station 120 estimates thesize {tilde over (Q)}_(k) ^(BS)(n) of the queue of the base station inwhich the data to be transmitted to the user (user K) based on thereceived information (S203).

The relay station 120 regards a packet arriving at the base station 110as a constant bit rate (CBR) packet, and periodically calculates thesize {tilde over (Q)}_(k) ^(BS)(n) of the virtual queue of the basestation and updates the estimation results by a certain time unit.

When the size of the virtual queue of the base station estimated at annth time is {tilde over (Q)}_(k) ^(BS)(n), the size of {tilde over(Q)}_(k) ^(BS)(n+1) of the virtual queue of the base station estimatedat an (n+1)th time may be expressed by Equation 11 shown below:{tilde over (Q)} _(k) ^(BS)(n+1)=max({tilde over (Q)} _(k) ^(BS)(n)−S_(k) ^(BS)(n),0)+Ã _(k) ^(RS)(n),k=1,2, . . . ,K  [Equation 11]

Thereafter, the relay station 120 determines the size of the virtualqueue obtained by adding the estimated size {tilde over (Q)}_(k)^(BS)(n) of the queue of the base station and the size Q_(k) ^(RS)(n) ofthe queue of the relay station in which the data to be transmitted fromthe relay station to the user is stored (S205).

The virtual queue is assumed to be a single virtual queue of the basestation obtained by adding the queue of the base station and the queueof the relay station. In a sense that the queue corresponds to a queuestoring the overall data to be transmitted to the user K, it may becalled a virtual queue. The size of the virtual queue is determined asexpressed by Equation 12 shown below:{tilde over (Q)} _(k) ^(BS)(n)+Q _(k) ^(RS)(n)  [Equation 12]

The relay station 120 performs scheduling for resource allocation basedon the size of the virtual queue (S207). Scheduling is performed by therelay station 120 on the user K as expressed by Equation 13 shown below:

$\begin{matrix}{{\gamma^{RS}(n)} = {\text{arg}{\max\limits_{{k = 1},\;...\;,\; K}{\gamma_{k}{R_{Rk}(n)}\left( {{(n)} + {Q_{k}^{RS}(n)}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

Thereafter, the relay station 120 determines resource allocationpriority based on the scheduling results and transfers the generateddata to the user (S209).

According to circumstances, the base station 110 may periodically orrandomly transmit the information regarding the size Q_(k) ^(BS)(n) ofthe queue of the base station storing the data to be transmitted to theuser to the relay station 120 (S211).

Upon receiving the information regarding the size Q_(k) ^(BS)(n) of thequeue of the base station storing the data to be transmitted to the userfrom the base station 110, the relay station 120 updates the informationregarding the size {tilde over (Q)}_(k) ^(BS)(n) of the queue of thebase station estimated in step S203 with the information regarding thesize Q_(k) ^(BS)(n) of the queue received from the base station (S215).

Thereafter, a scheduling process of the relay station is performed basedon the updated information regarding the size of the queue of the basestation (S217). Scheduling is performed by the relay station 120 on theuser as expressed by Equation 14 shown below:

$\begin{matrix}{{\gamma^{RS}(n)} = {\arg\;{\max\limits_{{k = 1},\;\ldots\;,K}{\gamma_{k}{R_{Rk}(n)}\left( {{Q_{k}^{BS}(n)} + {Q_{k}^{RS}(n)}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Thereafter, the relay station 120 determines resource allocationpriority of the user according to the scheduling results performed basedon the updated information regarding the size of the queue of the basestation, and transfers the generated data to the user (S219).

In FIG. 2, the signal transferred from the base station 110 may be theinformation Ã_(k) ^(BS)(n) regarding the amount of generated data to betransmitted to the user or the information Q_(k) ^(BS)(n) regarding thesize of the queue of the base station storing the data to be transmittedto the user, and here, it is described that the two items of informationare independently transmitted, but in a different embodiment of thepresent invention, the base station 110 may transmit both Ã_(k) ^(BS)(n)and Q_(k) ^(BS)(n) to the relay station 120 at a time. This will bedescribed in detail with reference to FIG. 3

FIG. 3 is a view showing a sequential scheduling process according to asecond embodiment of the present invention. Unlike the case of FIG. 2,in FIG. 3, the information Ã_(k) ^(BS)(n) and Q_(k) ^(BS)(n) istransmitted at an interval of a period Ta from the base station 110 tothe relay station 120.

The relay station 120 may periodically receive information regarding theamount of generated data to be transmitted to the user from the basestation 110 and estimates the size {tilde over (Q)}_(k) ^(BS)(n) of thequeue of the base station storing the data to be transmitted to theuser. The estimation of the size of the queue of the base station is thesame as described above with reference to FIG. 2.

Also, the base station 110 transmits the information regarding the sizeQ_(k) ^(BS)(n) of the queue of the base station storing the data to betransmitted to the user to the base station 120 at a Ta interval ofperiod (S301).

The relay station 120 periodically receives the information regardingthe size Q_(k) ^(BS)(n) of the queue of the base station from the basestation 110 and updates the size {tilde over (Q)}_(k) ^(BS)(n) of thequeue of the base station estimated previously with the size Q_(k)^(BS)(n) (S303).

Thereafter, the relay station 120 obtains the size of a virtual queuestoring the overall data to be transmitted to the user with reference tothe updated information regarding the size of the queue of the basestation and the size of the queue storing the data to be transmitted tothe user, and performs scheduling to allocate resource based on theobtained size of the virtual queue (S305).

Thereafter, the relay station 120 transmits data to the user based onthe scheduling results (S307).

In FIG. 3, information transferred from the base station is received atthe Ta interval of period, and thus, during a time between intervalsduring which the information transmitted by the base station isreceived, the relay station 120 performs a process of estimating thesize of the queue of the base station and updating the size of thevirtual queue (S309).

Referring to the updated size of the virtual queue, as described abovewith reference to Equation 11, when the size of the queue of the basestation at the nth time is Q_(k) ^(BS)(n), the size {tilde over (Q)}_(k)^(BS)(n+1) of the virtual queue of the base station estimated at the(n+1)th time is determined, based on which the size of the virtual queueis determined.

The base station 120 performs scheduling based on the size of thevirtual queue calculated at the (n+1)th time (S311) and transmits datato the user (S313).

Thereafter, when the relay station 120 receives information regardingthe size Q_(k) ^(BS)(n) of the queue of the base station storing data tobe transmitted to the user from the base station 110 at the Ta intervalof period again (S315), the relay station updates the size of thevirtual queue by using the received information regarding the size ofthe queue of the base station (S317), performs scheduling (S319), andthen, transmits data to the user (S321).

In the scheduling process performed by the relay station as describedabove with reference to FIG. 3, the relay station 120 periodicallyreceives the average arrival rate of the packets transferred from thebase station 110 or the size of the queue of the base station,determines the size of the virtual queue based on the same, and performsscheduling, but the base station 110 may aperiodically provides theinformation to the relay station 120. Namely, the base station 110 mayinform the base station 120 about the size of the queue of the basestation 110 under the condition that the size of the queue within thebuffer of the base station 110 arrives at a predetermined reference. Forexample, when the size of the queue of the base station 110 is changedat a certain rate or higher or when the average arrival rate is changedat a certain rate or higher, the base station 110 may transfer thecorresponding information to the relay station 120. This will bedescribed in detail with reference to FIG. 4.

FIG. 4 is a view showing a sequential scheduling process according to athird embodiment of the present invention.

When the size of the queue of the base station storing the data to betransmitted to the user corresponds with a predetermined reference, thebase station 110 transmits the information regarding the size of thequeue to the relay station 120 (S401).

When the size of the queue of the base station storing the data to betransmitted to the user is a certain value or greater or smaller, thebase station 110 may transmit the information regarding the size of thequeue.

The relay station 120 determines the size of the virtual queue storingthe overall data to be transmitted to the user or updates the previouslydetermined size of the virtual queue with reference to the informationregarding the size of the queue received from the base station and thesize of the queue storing the data to be transmitted to the user fromthe relay station (S403).

Based on the size of the virtual queue determined as described above,the relay station 120 performs scheduling to allocate resource (S405),and transmits data to the user based on the scheduling results (S407).

Thereafter, although the base station 110 does not transmit additionalinformation to the relay station 120 because the size of the queue ofthe base station 110 is be changed to be more than a certain rate or theaverage arrival rate is not changed to be more than a certain rate, therelay station 120 updates the size of the virtual queue for a datatransmission of a next time (S409), performs scheduling based on theupdated size of the virtual queue (S411), and transmits data to the user(S413).

When the size of the queue of the base station 110 is changed to be morethan a certain rate of when the average arrival rate is changed to bemore than the certain rate, the base station 110 transmits theinformation regarding the size of the queue of the base station storingthe data to be transmitted to the user to the relay station 120 again(S415). Thereafter, a scheduling operation of the relay station 120 isthe same as described above, so a repeated description thereof will beomitted.

According to another embodiment of the present invention, in order tosimply implement the scheduling operation of the relay station, the basestation 110 may determine scheduling priority of the relay station andprovide the corresponding information. This will be described in detailwith reference to FIG. 5.

FIG. 5 is a view showing a sequential scheduling process according to afourth embodiment of the present invention.

The base station 110 transmits user index information indicating thatthe amount of data to be transmitted to the user exceeds a certainreference to the relay station 120 (S501).

The user index information transmitted by the base station 110 may beindex information indicating an index of users whose amount of currentlyaccumulated packets is the largest based on the amount of packets to betransmitted by the base station 110 to the relay station 120, orindicating scheduling priority of each user with reference to the amountof packets currently accumulated in the queue of the base station.

According to circumstances, the base station 110 may determinescheduling priority of the relay station 120 and transmit thecorresponding priority.

The relay station 120 receives the user index information from the basestation 110 (S503), and performs scheduling to determine resourceallocation priority of each user with reference to the received userindex information and the size of the queue of the relay station storingthe data to be transmitted to the user from the relay station 120(S505).

According to circumstances, the relay station 120 may perform schedulingbased on the priority information transferred from the base station,rather than performing a scheduling algorithm.

Thereafter, the relay station 120 transmits data to the user based onthe scheduling results (S507).

FIG. 6 is a schematic block diagram of a scheduling apparatus of a relaycommunication system according to an embodiment of the presentinvention.

The scheduling apparatus includes a receiver 601, a controller 503including a virtual queue estimator 605 and a scheduler 607, and atransmitter 609.

The receiver 601 receives the amount of generated data to be transmittedto the user from the base station and information regarding the size ofa queue of the base station storing data to be transmitted to the user.

The virtual queue estimator 605 estimates the size of the queue of thebase station storing the data to be transmitted to the user based on theamount of generated data received from the base station, and determinesthe size of a virtual queue storing the overall data to be transmittedto the user with reference to the estimated size of the queue of thebase station and the size of the queue of the relay station storing datato be transmitted to the user.

The scheduler 607 performs scheduling to allocate resource based on thesize of the virtual queue determined by the virtual queue estimator 605.

The transmitter 609 transmits data to the user based on the schedulingresults from the scheduler 607.

According to another embodiment of the present invention, in order tolower implementation complexity of the controller 603, the receiver 601may receive user index information whose amount of data to betransmitted to the user exceeds a certain reference from the basestation, and the scheduler 607 may determine resource allocationpriority of each user with reference to the user index informationreceived from the base station and the size of the queue storing thedata to be transmitted from the relay station.

FIGS. 7 and 8 are graphs of performance comparison results showing delayviolation probability of a user according to a scheduling scheme.

FIG. 7 shows delay violation probability when all of the users areconnected to the relay station 120. In FIG. 7, (a) shows a case ofemploying max backlog scheduling, (b) shows a case of employing maxdifferential backlog scheduling, and (c) shows a case of employing maxtotal backlog scheduling according to an embodiment of the presentinvention.

Also, FIG. 7 shows the probability of exceeding a particular delay timeof five users when all of the five users are connected to the basestation 110 through the relay station 120. Namely, it means that when ascale in the x axis is 60 msec, if a scale in the y axis is 0.01, theprobability that a packet experiences delay of 60 msec or more is 1%.Also, in FIG. 7, it is assumed that packets of each user arrive at thebase station at 300 kbps and a signal-to-noise ratio (SNR) between thebase station and the relay station is 10 dB and SNRs between the relaystation and the respective users are 2, 3, 4, 5, and 6 dB, respectively.

When (a), (b), and (c) in FIG. 7 are compared, it can be seen that adelay time of the max total backlog scheme (c) proposed in the presentinvention is considerably reduced in comparison to the existing schemes(a) and (b).

FIG. 8 show delay violation probability when three users are connectedto the base station by way of the relay station and two users aredirectly connected to the user. SNRs of the two users directly connectedto the base station are 6 dB and 7 dB, respectively, and SNRs of thethree users connected to the relay station are 2 dB, 3 dB, and 4 dB,respectively.

In FIG. 8, (a) shows a case of employing max backlog scheduling, (b)shows a case of employing max differential backlog scheduling, and (c)shows a case of employing max total backlog scheduling proposed in thepresent invention.

It can be seen that, in case of max backlog and max total backlog, theusers directly connected to the base station have similar performance in(a), (b), and (c), while the performance of max differential backlog wasnot good. This is because the users connected to the base station by wayof the relay station are discriminated, as described above.

Also, it can be seen that the users connected by way of the relaystation have better performance of max total backlog than those of theother two schemes.

The method according to exemplary embodiments of the present inventiondescribed thus far may be implemented as software, hardware or acombination thereof. For example, the method according to exemplaryembodiments of the present invention may be stored in a storage medium(e.g., an internal memory, a flash memory, a hard disk, or the like),and may be implemented as codes or commands in a software program thatcan be executed by a processor (e.g., a microprocessor in a terminal).

The exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which like numbers referto like elements throughout. In describing the present invention, if adetailed explanation for a related known function or construction isconsidered to unnecessarily divert the gist of the present invention,such explanation has been omitted but would be understood by thoseskilled in the art. The accompanying drawings of the present inventionaim to facilitate understanding of the present invention and should notbe construed as limited to the accompanying drawings. The technical ideaof the present invention should be interpreted to embrace all suchalterations, modifications, and variations in addition to theaccompanying drawings.

The invention claimed is:
 1. A scheduling method of a relay station in arelay communication system, the method comprising: receiving informationregarding an amount of generated data to be transmitted to a user from abase station; estimating a size of a queue of the base station storingthe data to be transmitted to the user based on the amount of generateddata received from the base station; obtaining a size of a virtual queuein which overall data to be transmitted to the user with reference tothe estimated size of the queue of the base station and a size of aqueue of the relay station storing the data to be transmitted to theuser; performing scheduling to allocate resources based on the size ofthe virtual queue; and transmitting the data to the user based onresults of the scheduling performed, wherein when the estimated size ofthe queue of the base station is {tilde over (Q)}_(k) ^(BS)(n), the sizeof the queue of the relay station is Q_(k) ^(RS)(n), a channel linktransfer rate between the user and the relay station is R_(Rk)(n), and ascheduling constant value of the user is γ_(k), then, the schedulingγ^(RS)(n) is determined by the following Equation:${\gamma^{RS}(n)} = {\text{arg}{\max\limits_{{k = 1},\;...\;,\; K}{\gamma_{k}{R_{Rk}(n)}{\left( {{(n)} + {Q_{k}^{RS}(n)}} \right).}}}}$wherein each of n,k, and K is an integer.
 2. The method of claim 1,wherein the information regarding the amount of generated data receivedfrom the base station is average arrival rate information of a packet tobe transmitted to the user, and the average arrival rate information isperiodically received from the base station.
 3. The method of claim 1,wherein the estimating the size of the queue of the base stationcomprises: receiving further information regarding the size of the queueof the base station storing the data to be transmitted to the user fromthe base station; and updating the estimated information regarding thesize of the queue of the base station based on the received furtherinformation regarding the size of the queue of the base station.
 4. Ascheduling method of a relay station in a relay communication system,the method comprising: periodically receiving information regarding anamount of generated data to be transmitted to a user from a base stationto estimate a size of a queue of the base station storing the data to betransmitted to the user; periodically receiving the informationregarding the size of the queue of the base station storing the data tobe transmitted to the user from the base station to update the estimatedsize of the queue of the base station; obtaining a size of a virtualqueue storing overall data to be transmitted to the user with referenceto the updated size of the queue of the base station and a size of aqueue of the relay station storing the data to be transmitted to a theuser; performing scheduling to allocate resources based on the size ofthe virtual queue; and transmitting the data to the user based onresults of the scheduling performed, wherein when the updated size ofthe queue of the base station is Q_(k) ^(BS)(n), the size of the queueof the relay station is Q_(k) ^(RS)(n), a channel link transfer ratebetween the user and the relay station is RRk(n), and a schedulingconstant value of the user is γ_(k), then, the scheduling γ^(RS)(n) isdetermined by the following Equation:${\gamma^{RS}(n)} = {\arg\;{\max\limits_{{k = 1},\;\ldots\;,K}{\gamma_{k}{R_{Rk}(n)}{\left( {{Q_{k}^{BS}(n)} + {Q_{k}^{RS}\;(n)}} \right).}}}}$wherein each of n,k, and K is an integer.
 5. A scheduling method of arelay station in a relay communication system, the method comprising:receiving information regarding a size of a queue of a base stationstoring data to be transmitted to a user from the base station when thesize of the queue of the base station corresponds to a predeterminedreference; obtaining a size of a virtual queue storing overall data tobe transmitted to the user with reference to the information regardingthe size of the queue of the base station received from the base stationand a size of a queue of the relay station storing the data to betransmitted to the user; performing scheduling to allocate resourcesbased on the size of the virtual queue; and transmitting the data to theuser based on results of the scheduling performed, wherein when theupdated size of the queue of the base station is Q_(k) ^(BS)(n), thesize of the queue of the relay station is Q_(k) ^(RS)(n), a channel linktransfer rate between the user and the relay station is RRk(n), and ascheduling constant value of the user is γ_(k), then, the schedulingγ^(RS)(n) is determined by the following Equation:${\gamma^{RS}(n)} = {\arg\;{\max\limits_{{k = 1},\;\ldots\;,K}{\gamma_{k}{R_{Rk}(n)}{\left( {{Q_{k}^{BS}(n)} + {Q_{k}^{RS}(n)}} \right).}}}}$wherein each of n,k, and K is an integer.
 6. The method of claim 5 theinformation regarding the size of the queue of the base station isreceived from the base station when the size of the queue of the basestation storing the data to be transmitted to the user is greater thanor smaller than a predetermined value.
 7. A scheduling apparatus of arelay station in a relay communication system, the apparatus comprising:a receiver configured to receive an amount of generated data to betransmitted to a user and information regarding a size of a queue of abase station storing the data to be transmitted to the user from thebase station; a virtual queue estimator configured to estimate the sizeof the queue of the base station storing the data to be transmitted tothe user based on the amount of generated data received from the basestation and to determine a size of a virtual queue storing overall datato be transmitted to the user with reference to the estimated size ofthe queue of the base station and a size of a queue of the relay stationstoring the data to be transmitted to the user; a scheduler configuredto perform scheduling to allocate resources based on the size of thevirtual queue determined by the virtual queue estimator; and atransmitter configured to transmit the data to the user based on resultsof the scheduling performed by the scheduler, wherein when the estimatedsize of the queue of the base station is {tilde over (Q)}_(k) ^(BS)(n),the size of the queue of the relay station is Q_(k) ^(RS)(n), a channellink transfer rate between the user and the relay station is R_(Rk)(n),and a scheduling constant value of the user is γ_(k), then, thescheduling γ^(RS)(n) is determined by the following Equation:${\gamma^{RS}(n)} = {\text{arg}{\max\limits_{{k = 1},\;...\;,\; K}{\gamma_{k}{R_{Rk}(n)}{\left( {{(n)} + {Q_{k}^{RS}(n)}} \right).}}}}$wherein each of n,k, and K is an integer.
 8. The apparatus of claim 7,wherein the receiver is further configured to receive user indexinformation of a user whose amount of data to be transmitted to the userfrom the base station exceeds a predetermined reference, and thescheduler is further configured to determine a resource allocationpriority of each user with reference to the user index informationreceived from the base station and the information regarding the size ofthe queue of the base station storing the data to be transmitted to theuser received from the base station.